SANGER, Calif. — The shabby farmhouse tucked behind vineyards hardly looked like a clandestine factory for California's most elusive drug makers. It blended perfectly into this rural San Joaquin Valley town, right down to the children on the lawn, the chickens in coops and the vans to transport farm workers.

Only a red stain eating away at the metal roof hinted at its real purpose. In January, drug agents stormed inside and found an all-too-familiar scene:

A makeshift lab containing enough tubes, huge flasks and burners to cook hundreds of pounds of methamphetamine--a white crystalline stimulant known as crank or speed, fancied as a bargain substitute for cocaine.

This time, like most times, the cook was gone and the farm workers there weren't talking. Fifty pounds of meth, one night's toil worth $2.5 million on the streets of Chicago, already was 100 miles down the interstate--California's newest exported crop.

Once the domain of outlaw biker gangs, the nation's meth trade has been taken over by Mexican drug families in the rural belt from San Diego County to Redding. Operating from Sinaloa and other states deep inside Mexico, these families oversee teams of cookers dispatched to orchards, cotton fields, chicken ranches and abandoned dairies north of the border.

Their ability to produce the drug in mass quantities overnight and distribute it across the country in days is one of the most perplexing problems to confront local, state and federal authorities.

"In my 24 years in law enforcement, I've never seen a drug problem as frustrating as this one," said John Coonce, who heads the Drug Enforcement Administration's national clandestine meth lab task force in Washington. "It is absolutely epidemic."

Toxic byproducts of the labs are being dumped in canals, fields and streams, posing a growing environmental hazard. The bullet-riddled bodies of farm labor contractors and workers who moonlight in meth labs are showing up in fields. Agents say that the motive for these murders is not always clear but that the message is unmistakable to anyone thinking of crossing the rings.

The labs, like the one in Sanger, may be makeshift but they are highly efficient, mobile and hard to spot. Unlike the small-time biker operations, the Mexican-run labs betray little chemical smell. Often, agents are alerted to a lab only after a shed or house explodes.

The cookers blend in with the seasonal ebb and flow of farm laborers, moving with virtual impunity.

"The Mexicans do it so simply, so quickly and their network is so mobile and tight that they can make meth today and have it sold in the Midwest tomorrow," said Wilfredo Cid, head of the state Bureau of Narcotic Enforcement's office in the San Joaquin Valley, where the bigger labs seem to be moving.

The lure for meth producers is obvious. Mexico's drug syndicates long have had to split their cocaine, heroin and marijuana profits with growers, middlemen and mules ferrying the product north. But meth, made and sold in the U.S.A., is the closest thing to pure profit they have found.

Mexican nationals are smuggling meth to virtually every state and commanding premium prices, according to state and federal drug agents. In Florida, for example, California meth sells for five times what it does here.

Because the rings delegate tasks, agents are seldom able to snare more than one head of the Mexican meth Hydra. Consider three busts on the same day last month in Southern California.

First, a sheriff's narcotics agent was summoned to the Riverside County community of Menifee to inspect a suspicious Ford van pulled over after running a stop sign. Inside, he found enough chemicals sloshing in plastic containers to make more than 120 pounds of crystal meth with a wholesale value of $600,000.

The ring had split the manufacturing process between two labs to thwart authorities; the driver refused to disclose either site.

Later that morning, in the northern San Diego County town of Fallbrook, state agents smelled telltale odors wafting from a large shed. Inside, they found sophisticated lab ware and enough chemicals to cook about 30 pounds of meth, but no leads to higher-ups.

About the same time, agents acting on a tip raided a handsome home in Montclair in San Bernardino County and found enough hydriodic acid to make 300 pounds of meth. Only a middleman was arrested, authorities said.

Methamphetamine, a central nervous system stimulant, once was used by long-haul truckers and college students pulling all-nighters. Today, because it creates effects similar to cocaine but longer lasting, it is injected, snorted or smoked by partying teen-agers, housewives who want to lose weight, laborers seeking to increase productivity and professionals hoping to cram more into their day and to enhance sexual performance at night.